Thermoplastic compositions of watersoluble cellulose ethers



United rates Patent Q THERMOPLASTIC CGMPOSITIONS OF WATER- SOLUBLECELLULOSE'ETHERS Earle L. Kropscott and George K. Greminger, Jr.,Midland, and Miles A. Weaver, Ithaca, Mich., assignors to The DowChemical Company, Midland, Mich., a corporation of Delaware No Drawing.Application November 25, 1953 Serial No. 394,506

8 Claims. (Cl. 106-182) This invention relates to thermoplastic,water-soluble compositions of certain cellulose ethers.

Methods for fabricating useful articles from water- 'soluble celluloseethers have been limited to casting and dipping from aqueous solutions.Because of the unique solubility characteristics of those ethers manydifliculties arose when it was attempted to use such methods. Forexample, the temperature of the solution had to remain below the gelpoint of the cellulose ether during the shaping operation. Anotherobjection was that the amount of cellulose ether in solution had to berestricted, because the viscosity of the solution had to be low enoughfor casting or dipping operations. A still further objection was thedifficulty in dissolving sufficient amounts of the higher viscositygrades of the ethers. Therefore, so that the cellulose ethers may beused in a wider variety of applications for which their properties areideally suited, it has long been desired to find a thermoplasticwatersoluble cellulose ether composition which could be thermallyfabricated. One such composition has been disclosed by Silvernail in U.S. Patent 2,602,755. That composition consisted of a water-solublecellulose ether, propylene glycol, and glycerine in certain statedproportions.

It is an object of this invention to provide water-soluble compositionsof cellulose ethers, which compositions are capable of being thermallyfabricated.

It has now been found that thermoplastic compositions may be prepared bymixing or blending certain watersoluble cellulose ethers with an alkyllactate in which the alkyl group contains from 1 to 4 carbon atoms.Although these compositions are especially well adapted for thermalfabrication, they may also be used in conventional casting and dippingoperations.

The cellulose ethers that are useful in the compositions of thisinvention are water-soluble alkyl, hydroxyalkyl, or alkyl hydroxyalkylcellulose ethers in which the alkyl group may contain from 1 to 3 carbonatoms and in which the hydroxyalkyl group may contain from 2 to 3 carbonatoms. Of particular usefulness are methyl cellulose, hydroxypropylcellulose, and methylhydroxypropyl cellulose.

It is not critical in the compositions of this invention that theaforementioned ethers exhibit thermoplasticity in themselves. The chiefrequirement for use in this invention, besides the previously mentionedstructural limitations, is water solubility. It is well-known thatmethyl cellulose, and other cellulose ethers which are soluble inaqueous media, differ in their solubility properties depending on theextent to which they are etherified. The least etherified products aresoluble only in dilute alkaline media, and often only at lowtemperatures. The somewhat more highly etherified materials are solublein water. In a few cases the fully etherified compounds become insolublein water and are soluble only in organic solvents. Also, certain alkylhydroxyalkyl cellulose ethers, such as those described in our copendingap- 2 plication Serial No. 394,484, filed November 25, 1953, are solublein both aqueous and organic media.

Any of the-commercially available viscosity grades of these celluloseethers may be employed. The viscosity grade used will depend chiefly'onthe properties desired in the fabricated article and on other practicalconsiderations such the length of time required 'to blend the etherswith the plasticizer. The higher the intrinsic viscosity of thecellulose ether, the less fluid will be the composition and the longerwill be the time required to mix in the plasticizer.

As previously mentioned, the useful plasticizer for the compositions ofthis invention are alkyl lactates in which the alkyl group contains from1 to 4 carbon atoms. When the alkyl groups contain five or more carbonatoms, the

solvent power ofthe alkyl lactate is-decreased to the'point where theyno longer are useful as-plasticizers. Other known plasticizers forcellulose ethers may be used in conjunction with the alkyl lactates ofthis invention. As examples of such plasticizers may be mentionedpropylene glycol, the esters of glycollic acid, and acetyl tributylcitrate. Their use is not essential, however, in preparing thethermoplastic compositions.

The amount of plasticizer that may be employed in the compositions mayvary within wide limits between 20 and percent, preferably from 20 to 85percent. The amount that is used in any particular composition willdepend on the viscosity grade of the cellulose derivative, and on theintended use of the composition. It should be obvious that when the veryhigh viscosity grades of cellu- I lose ethers (4000 centipoises orhigher) are used, high concentrations of the cellulose ether areimpractical because the resultiug solutions are so viscous that theycannot be easily worked. Also, the fluidity of the plasticizedcomposition that is necessary varies with the type of fabricatingoperation. For casting and dipping operations, the solutions must havegreater fluidity than with most thermal operations, such as injectionmolding or extrusion. When reference is made herein to the viscositygrade of the cellulose ether, this is the viscosity in centipoises of a2 percent solution of that ether by weight in water at 20 C.

The compositions of the invention will be further defined by thefollowing illustrative examples.

Example 1 A composition was prepared consisting of 20 parts by weight ofa water-soluble methyl hydroxypropyl cellulose cps. viscosity grade) and80 parts by weight of ethyl lactate. The mixture was heated to 140 C.with agitation to effect solution. The resulting composition wasuniformly clear with no evidence of gels.

When the above composition was subjected to extrusion conditions, aclear, flexible strip was obtained.

In a like manner similar compositions were prepared using propyl andbutyl lactates in place of the ethyl lactate. These compositions couldbe extruded to produce clear and flexible strips or sheets.

Example 2 Compositions were prepared consisting of 50 parts by weight ofa water-soluble methyl cellulose 50 cps. viscosity grade) and 35 partsby Weight of ethyl lactate and 15 parts by Weight of acetyl tributylcitrate. The mixture was heated to C. with agitation to effect solution.The resulting composition formed clear strips when sub jected to thermalextrusion conditions. The strips were placed in a cavity type die andpharmaceutical capsules prepared by vacuum drawing the strips into themolds. The capsules produced were comparable to the common gelatincapsules.

Example 3 A composition consisting of 15 parts by weight of awater-soluble hydroxyethyl cellulose, 45 parts by weight ofisobutyl'lactate, and 40 parts by weight of propylene glycol wasprepared. Capsules were prepared by dipping V brass pins into thesolution which was heated to 140 C. to obtain the required dippingfluidity. The capsules were then cooled and stripped from the pins. Theywere tough, and were readily soluble in water, and were deemed tobesuperior to the common gelatin capsules.

1. A thermoplastic composition consisting essentially selected from thegroup of alkyl cellulose, hydroxyalkyl cellulose, and alkyl hydroxyalkylcellulose in which the alkyl group contains from 1 to 3 carbon atoms andthe .hydroxyalk'yl group contains from 2 to 3 carbon atoms,

and correspondingly-from 95 to 20'percent of an alkyl lactate in whichthe alkyl group contains from 1 to 4 carbon atoms as a permanentplasticizer for said water-soluble cellulose ether. I

, of from 5 to 80' percent of a water-soluble cellulose ether 2..Ihecomposition claimed in claim 1, wherein the cellulose ether is awater-soluble methyl cellulose.

3. The composition claimed in claim 1, wherein the cellulose ether is awater-soluble methyl hydroxypropyl cellulose. 1 W

4. The composition claimed in claim l, wherein the cellulose ether is awater-soluble hydroxyethyl cellulose.

5. The composition claimed inclaim l, 'whereinthe alkyl lacetate isethyl lactate.

6. The'composition claimed in claim 1, Whereint he alkyl lactate is'propyl lactate.

7. The composition claimed in claim 1, alkyl lactate is butyl lactate.

8 The composition claimed in claim 1, wherein the alkyl lactate isisobutyl lactate.

wherein the References Cited in the file of this patent:

1. A THERMOPLASTIC COMPOSITION CONSISTING ESSENTIALLY OF FROM 5 TO 80PERCENT OF A WATER-SOLUBLE CELLULOSE ETHER SELECTED FROM THE GROUP OFALKYL CELLULOSE, HYDROXYALKYL CELLULOSE, AND ALKYL HYDROXYALKYLCELLULOSE IN WHICH THE ALKYL GROUP CONTAINS FROM 1 TO 3 CARBON ATOMS ANDTHE HYDROXYALKYL GROUP CONTAINS FROM 2 TO 3 CARBON ATOMS, ANDCORRESPONDINGLY FROM 95 TO 20 PERCENT OF AN ALKYL LACTATE IN WHICH THEALKYL GROUP CONTAINS FROM 1 TO 4 CARBON ATOMS AS A PERMANENT PLASTICIZERFOR SAID WATER-SOLUBLE CELLULOSE ETHER.